Untreated surfaces of molded rubber comprising non-polar elastomers such as natural rubber, polyisoprene, polybutadiene, thermoplastic elastomers, and styrene butadiene, including blends often exhibit inadequate adhesion to adhesives and coatings. Even though an adhesive or coating may have excellent bond strength to a non-elastomer substrate material such as a metal, fiber, wood, or glass, in bonding of those substrates to such surfaces of cured elastomers, the composite article can delaminate under mechanical stress, the influence of chemical agents such as salt, solvents, etc., weathering, or a combination of factors.
Accordingly, various primers and pretreatments treatments have so far been performed on the surface of the shaped rubber articles used as a base material. Surface chlorination of rubber has long been proposed for the improving adhesion, reducing tackiness and decreasing the coefficient of friction of rubber. (See Romberg, “Aqueous Chlorination of Natural Rubber Surfaces”, A.C.S. Rubber Division, Spring Meeting (1986); T.C.Q. Noakes, Proc. Int. Rubb. Technol. Conf., Penang, Malaysia (1988); Natural Rubber Technical Information Sheet No. 17, The Malaysian Rubber Producers' Research Association, Latex Series (1977); D. C. Blackley, “High Polymer Latices”, Palmerton Publishing Company (1966), p. 548, and PCT/GB92/00171, published as WO 92 13497.
It is known to treat elastomer surfaces with sulfuric acid, or hypochlorite such as alkyl hypohalite, e.g., t-butyl hypochlorite or t-butyl hypobromite. See U.S. Pat. No. 3,940,548.
It is also known from British Patent specification Nos. 1,295,677 and 1,293,842 to use halogenation donors. The halogenation donors proposed are in general chlorine donors such as trichloroisocyanuric acid, dibromodimethylhydantoin, and N-halogen sulphonamide such as N-chloroparatoluenesulphonamide.
Adhesion of adhesives and coatings to molded rubber surfaces can be interfered with by a variety of components used in the rubber formulation, in the molding operation, or dressings applied to finished rubber articles. Interference with adhesion of coatings can be due to such components as sulfur, accelerators, waxes, process oils, plasticizer, antioxidants, antiozonants, mold releases, and silicone dressings, to name a few. Adhesion of coatings can be improved by mechanical abrading but this has obvious drawbacks including non-uniform bonding strength and loss of smooth glossy finish.
A well known treating agent containing a chlorinating agent is available from Lord Corporation under the Chemlok® 7701 designation. Proper steps need to be taken by cleaning the rubber surface prior to applying this product. An improvement would be desirable from the standpoint preparing a molded rubber surface in one step. It would be further advantageous to provide surface preparation materials that are not classified as hazardous air pollutants.